1. Field of the Invention
The present invention relates to an image reading device, and a technique of preventing saturation of an output value of an image pick-up section in a case of imaging light radiated by a light source and reflected from a document surface.
2. Description of the Related Art
An image reading device using three colors of LEDs, a red LED, a blue LED, and green LED, for a light source as a means for illuminating a document is conventionally known. In the image reading device of a configuration such as above, as a means for controlling a light amount of each of the red LED, the blue LED, and the green LED, a technique of having any one of the LEDs of the red LED, the blue LED, and the green LED as a reference light source, and controlling the light amount of the other two LEDs with the light amount of the reference light source as a reference, is known.
However, an LED has many variations in a light amount as compared with other light sources such as a xenon lamp. In a case of the conventional image reading device described above, when there is a variation in the light amount of the reference LED (reference light amount) among the red LED, the blue LED, and the green LED, a light amount as an entire light source is significantly different between the reference LED having a maximum reference light amount and the reference LED having a minimum reference light amount. For example, in a case of the reference LED having the maximum reference light amount, a range of an amount of light which can be detected in an image pick-up section (for example, a CCD) is exceeded, and this causes a problem that an output value in the image pick-up section is saturated (data of the amount exceeding the range is lost).